Method for growing conformal EPI layers and structure thereof

Abstract

A method for forming a conformal buffer layer of uniform thickness and a resulting semiconductor structure are disclosed. The conformal buffer layer is used to protect highly-doped extension regions during formation of an epitaxial layer that is used for inducing mechanical stress on the channel region of transistors.

What is claimed is: 
     
       1. A semiconductor structure comprising:
 a first transistor and a second transistor disposed on a silicon substrate, wherein the first transistor and second transistor each comprise an extension region formed within the silicon substrate; 
 an opening in the silicon substrate between the first transistor and second transistor; 
 a conformal buffer layer of uniform thickness disposed within the opening, and covering a side of each extension region; and 
 an epitaxial layer formed within the opening, and in contact with the buffer layer, 
 wherein the epitaxial layer extends alongside, below, and underneath the buffer regions. 
 
     
     
       2. The semiconductor structure of  claim 1 , wherein the buffer layer is comprised of a boron-doped SiGe film comprising a boron dopant concentration ranging from about 1E19 atoms/cm3 to about 5E19 atoms/cm3, and wherein the epitaxial layer is comprised of a boron-doped SiGe film comprising a boron dopant concentration ranging from about 1E20 atoms/cm3 to about 9E20 atoms/cm3. 
     
     
       3. The semiconductor structure of  claim 1 , wherein the buffer layer is comprised of an undoped SiGe film, and wherein the epitaxial layer is comprised of a boron-doped SiGe film comprising a boron dopant concentration ranging from about 1E20 atoms/cm3 to about 9E20 atoms/cm3. 
     
     
       4. The semiconductor structure of  claim 1 , wherein the buffer layer is comprised of an undoped silicon-carbon film, and wherein the epitaxial layer is comprised of a phosphorous-doped silicon-carbon film comprising a phosphorous dopant concentration ranging from about 1E20 atoms/cm3 to about 9E20 atoms/cm3. 
     
     
       5. The semiconductor structure of  claim 1 , wherein the buffer layer is comprised of a SiGe material with a germanium content in the range of about 30 percent to about 60 percent, and wherein the epitaxial layer is comprised of a boron-doped SiGe film comprising a boron dopant concentration ranging from about 1E20 atoms/cm3 to about 9E20 atoms/cm3. 
     
     
       6. The semiconductor structure of  claim 1 , wherein the top of the buffer layer is higher than the top of silicon substrate. 
     
     
       7. The semiconductor structure of  claim 6 , wherein the epitaxial layer is non-faceted.